Nicole - who tells her story tonight on SBS's 'Insight: Unplanned' - didn't think about it again, until doctors told her she was pregnant.

"I was under the impression he'd worn a condom when we had sex," the now-31-year-old tells whimn.com.au, recalling the "complete shock" at the news.

"I'd had a couple of one-night stands or casual encounters and I had always been extremely careful. It wasn't something I was willing to do at that point in my life - I wasn't thinking of having a child any time soon. I remember telling him I wasn't on the pill that night."

But when Nicole abruptly found herself at this crossroads, things changed. She had terminated a prior pregnancy a few years earlier, but this time felt like there "wasn't a choice".

"I don't know why, I just couldn't fathom not keeping the baby. I just really felt like that was what I going to do," she says, "it's very hard to explain".

"From the very beginning, I knew there was a strong possibility I would have to do it absolutely, entirely by myself."

But in the next few weeks her curiosity began to peak about the man who would be the father of her child, who she knew almost nothing about, apart from his first name.

She couldn't even recall the suburb she'd woken up in that seemingly insignificant morning. But there was still a nagging sense of responsibility to track him down, she recalls, something she puts down to a society-entrenched ideology that a father has an "ethical right" to know.

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"People have a lot of opinions but I had that deeply ingrained in me so I was thinking, 'I have to find this guy': I had his first name and what he looked like in my mind."

She recalls putting his "very common" first name into Facebook. "I think I maybe scrolled through 100 photos a couple of times and then one day it was him, standing there in the same t-shirt he was wearing the night we met," she says, "and that's the person who I believe is the father of my child."

"When I saw his face I felt really scared, I had a bit of a panic attack about how this was going to change our whole life."

So, after scrolling through his social media - and coming across some things she found "a bit iffy" - she made a decision not to tell him.

"Obviously looking at someone's social isn't foolproof, but it seemed that we had quite differing value systems. I had to think about every possible scenario that could happen from telling him and the effect on his life and mainly the effect on my daughter's life. This is someone who could be a good thing or this could be someone who doesn't want anything to do with her and has a lot of anger about the situation."

Ultimately, she decided the latter scenario outweighed any possible positives.

"If he doesn't want anything to do with her, which is a high possibility, I then have to move on with my life, lying to my child which I never ever wanted to do or her growing up with the knowledge that her biological father doesn't want anything to do with her which is an extremely horrible thing to have to think."

Instead, she made the decision she would let her daughter, now almost four, make her own decision when she was old enough.

"I have all the details that I would need to find him in the future and if that's something she wants to do then I will fully support her and we will do it as a team, like we've done everything as a team. I'm not closed off to that option at all but I think that's a choice she has to make."

Unsurprisingly, Nicole says she is often confronted with others' judgements and opinions about her choice to have a baby she doesn't know and her choice not to tell him. She also says the lack of child support means they don't live a very rich existence".

But she has no doubt she made the right choice.

"I have no regrets or shame around the decision I made. I'm 100 percent happy that it was the right one for us."